Many residential buildings, especially older ones, have legacy cable infrastructures that can make it difficult to cost-effectively distribute high-bandwidth services. Residents of such buildings, desiring high-definition (HD) video and/or high-speed data communication services, can rely on channel stacking systems to leverage existing cable infrastructures for providing these modern services.
As shown in FIG. 1, a channel stacking system 1200 may receive a plurality of signals 1210 from M sources 1205. In the typical channel stacking system, the signal sources are satellites, however, such signals may be provided by other sources. Each signal 1210 may contain multiple channels of information which are frequency division multiplexed within a given bandwidth. Each band is typically modulated on an RF carrier frequency, which may or may not be common among the sources. Based upon control signals 1225 provided by receivers 1215, the channel stacking system 1200 will process the incoming signals 1210 and extract channels of interest. The extracted channels will then be assembled (i.e., stacked) into a new composite signal 1220 suitable for transmission along a single cable. This is sometimes referred to as sequencing the channels. The channels of the composite signal 1220 are also frequency division multiplexed so that each of the receivers 1215 (which are configured to receive programming at a designated frequency within the composite signal 1220) may receive the channel requested by its respective user via the control signals 1215.
In FIG. 2, further details are presented which exemplify the signal processing operations of a conventional channel stacking system receiver 1230. A plurality of RF signals 1232 may be received by one or more antennas (not shown) and passed to an analog preprocessing stage 1233. The analog preprocessing stage initially amplifies the received signals with one or more low noise amplifiers, and then band-pass filters the entire band to reject out of band noise. The signals are then provided to a first analog downconversion stage 1234, which downconverts each signal to relatively lower RF signal (e.g., from Ku-band to L-band). This lower RF signal is then coupled to a second analog downconversion stage 1236 which downconverts the signal to an intermediate frequency (IF) fIF using analog techniques. The output from the analog downconversion stage 1236 is shown in a magnitude response diagram 1246 of FIG. 2. In one embodiment, the downconverted signals are then digitized by an analog-to-digital converter stage 1238. The digitized signals are then provided to a digital switching and filtering/selection stage 1240. In this stage, a digital switch (not shown) selects the appropriate signal source based upon the desired channel. Once the appropriate signal source is selected, digital filters (not shown) are used to extract the channel of interest, as shown in a magnitude response diagram 1248 of FIG. 2. The signals are then passed to an upconversion and digital-to-analog conversion stage 1242 which translates each selected channel to an appropriate output frequency foR, as shown in a magnitude response diagram 1250 of FIG. 2. The output frequency for each channel is selected to correspond to the frequency assigned to the requesting receiver. Each upconverted channel is then assembled (sequenced) into a composite signal using an analog summer. The composite signal, an example of which is shown in a magnitude response diagram 1252 of FIG. 2, is centered at fo and has a bandwidth appropriate for transmission along a single cable.
As noted above, present channel stacking system satellite receivers typically employ multiple downconversion processes. For example, a conventional channel stacking system receiver may employ a two stage downconversion process; a first downconversion in the low noise block (LNB) stage, and a second downconversion at the IF stage. Multi-downconversion systems typically suffer from the disadvantages of increased circuit complexity and high power consumption.
Furthermore, as described above, selecting and extracting channels from multiple sources (e.g., satellites) and assembling these channels into a desired sequence presently employs analog techniques. Such processing is more advantageously done in the digital domain without the need for bandpass filtering or Hilbert Transformers.